HDR for skybox material

Hello

Is it possible to use a HDR image for a skybox like directly?

Or a sphere with a transparent layer and clouds?

Vivienne

I don’t believe Urho supports any image formats with hdr?

The way that I’ve gone about it is encoding the hdr information into the texture using an encoding:

Here is a fork of cmft with the ability to export dds with ‘bgrd8’, ‘bgrm8’ and ‘bgre8’ encodings:
github.com/hdunderscore/cmft/tree/hdr

Here is the hlsl shader code to decode them:

[code]float4 DecodeBGRM8(in float4 rgbm)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float M = exp2(rgbm.a / scale);
float m = M / (255.0f * 255.0f);
r.rgb = rgbm.rgb * m;
r.a = M;
return r;
}

#define DecodeHDR(IN) DecodeBGRM8((IN))
float4 DecodeBGRE8(in float4 rgbe)
{
float4 r;
r.a = rgbe.a * 255 - 128;
r.rgb = rgbe.rgb * exp2(r.a);
r.a = length(r.rgb);
return r;
}

float4 DecodeBGRD8(in float4 rgbd)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float D = MaxValue / exp2(rgbd.a / scale);
float d = D / (255.0f * 255.0f);
r.rgb = rgbd.rgb * d;
r.a = D;
return r;
}[/code]

This method doesn’t support alpha as the alpha channel being used for hdr on encoding.

2 Likes

[quote=“hd_”]I don’t believe Urho supports any image formats with hdr?

The way that I’ve gone about it is encoding the hdr information into the texture using an encoding:

Here is a fork of cmft with the ability to export dds with ‘bgrd8’, ‘bgrm8’ and ‘bgre8’ encodings:
github.com/hdunderscore/cmft/tree/hdr

Here is the hlsl shader code to decode them:

[code]float4 DecodeBGRM8(in float4 rgbm)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float M = exp2(rgbm.a / scale);
float m = M / (255.0f * 255.0f);
r.rgb = rgbm.rgb * m;
r.a = M;
return r;
}

#define DecodeHDR(IN) DecodeBGRM8((IN))
float4 DecodeBGRE8(in float4 rgbe)
{
float4 r;
r.a = rgbe.a * 255 - 128;
r.rgb = rgbe.rgb * exp2(r.a);
r.a = length(r.rgb);
return r;
}

float4 DecodeBGRD8(in float4 rgbd)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float D = MaxValue / exp2(rgbd.a / scale);
float d = D / (255.0f * 255.0f);
r.rgb = rgbd.rgb * d;
r.a = D;
return r;
}[/code]

This method doesn’t support alpha as the alpha channel being used for hdr on encoding.[/quote]

I think I understand. I have not used the hlsl shader so Im not sure how to use it.

Here is the change you would make for the skybox.hlsl (however you will need to make the adjustments for glsl yourself):

[code]#include “Uniforms.hlsl”
#include “Samplers.hlsl”
#include “Transform.hlsl”

#define DecodeHDR(IN) DecodeBGRM8((IN))

float4 DecodeBGRM8(in float4 rgbm)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float M = exp2(rgbm.a / scale);
float m = M / (255.0f * 255.0f);
r.rgb = rgbm.rgb * m;
r.a = M;
return r;
}

float4 DecodeBGRE8(in float4 rgbe)
{
float4 r;
r.a = rgbe.a * 255 - 128;
r.rgb = rgbe.rgb * exp2(r.a);
r.a = length(r.rgb);
return r;
}

float4 DecodeBGRD8(in float4 rgbd)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float D = MaxValue / exp2(rgbd.a / scale);
float d = D / (255.0f * 255.0f);
r.rgb = rgbd.rgb * d;
r.a = D;
return r;
}

void VS(float4 iPos : POSITION,
out float4 oPos : POSITION,
out float3 oTexCoord : TEXCOORD0)
{
float4x3 modelMatrix = iModelMatrix;
float3 worldPos = GetWorldPos(modelMatrix);
oPos = GetClipPos(worldPos);

oPos.z = oPos.w;
oTexCoord = iPos.xyz;

}

void PS(float3 iTexCoord : TEXCOORD0,
out float4 oColor : COLOR0)
{
float4 sky = DecodeHDR(texCUBE(sDiffCubeMap, iTexCoord.xyz));
sky.rgb *= sky.a;
sky.rgb *= cMatEnvMapColor.r;
oColor = (cMatDiffColor * sky);
}
[/code]

You would then need to use an encoded texture for the sky. The cMatEnvMapColor red channel affects the exposure.

BC6H is the HDR format that should be used, although GL2.1/DX9 doesn’t support it:
opengl.org/registry/specs/A … n_bptc.txt

Cadaver how is Turso3D these days? :slight_smile:

[quote=“boberfly”]BC6H is the HDR format that should be used, although GL2.1/DX9 doesn’t support it:
opengl.org/registry/specs/A … n_bptc.txt

Cadaver how is Turso3D these days? :slight_smile:[/quote]

Ah. Good to know. I sitll have to find a way to convert a hdr to dds.

How did you use it? I would have to use it from the command line.

[quote=“hd_”]I don’t believe Urho supports any image formats with hdr?

The way that I’ve gone about it is encoding the hdr information into the texture using an encoding:

Here is a fork of cmft with the ability to export dds with ‘bgrd8’, ‘bgrm8’ and ‘bgre8’ encodings:
github.com/hdunderscore/cmft/tree/hdr

Here is the hlsl shader code to decode them:

[code]float4 DecodeBGRM8(in float4 rgbm)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float M = exp2(rgbm.a / scale);
float m = M / (255.0f * 255.0f);
r.rgb = rgbm.rgb * m;
r.a = M;
return r;
}

#define DecodeHDR(IN) DecodeBGRM8((IN))
float4 DecodeBGRE8(in float4 rgbe)
{
float4 r;
r.a = rgbe.a * 255 - 128;
r.rgb = rgbe.rgb * exp2(r.a);
r.a = length(r.rgb);
return r;
}

float4 DecodeBGRD8(in float4 rgbd)
{
float4 r;
const float MaxRange = 20.0f;
const float MaxValue = 255.0f * MaxRange;
const float scale = 1.0f / log2(MaxValue);
float D = MaxValue / exp2(rgbd.a / scale);
float d = D / (255.0f * 255.0f);
r.rgb = rgbd.rgb * d;
r.a = D;
return r;
}[/code]

This method doesn’t support alpha as the alpha channel being used for hdr on encoding.[/quote]